# CVE-2026-31951: LibreChat's MCP Server Header Injection Enables OAuth Token Theft

> Attackers can steal OAuth tokens by creating malicious MCP servers with crafted headers, allowing account takeover in LibreChat.

- **Severity:** Medium 6.8 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 27 Mar 2026
- **Updated:** 31 Mar 2026
- **Also known as:** GHSA-pmw7-gqwj-f954

## What is CVE-2026-31951?

CVE-2026-31951 is a medium-severity vulnerability in Librechat Librechat, published on 27 Mar 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.

### Official description

LibreChat is a ChatGPT clone with additional features. In versions 0.8.2-rc1 through 0.8.3-rc1, user-created MCP (Model Context Protocol) servers can include arbitrary HTTP headers that undergo credential placeholder substitution. An attacker can create a malicious MCP server with headers containing `{{LIBRECHAT_OPENID_ACCESS_TOKEN}}` (and others), causing victims who call tools on that server to have their OAuth tokens exfiltrated. Version 0.8.3-rc2 fixes the issue.

Weakness: CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor)

## Which versions are affected by CVE-2026-31951?

It affects 1 product.


Products: Librechat Librechat.

## How do I fix CVE-2026-31951?

No fix has been published for CVE-2026-31951 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-31951 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-31951 exists.

## Other vulnerabilities in Librechat Librechat

- [CVE-2026-32625](https://insights.sbomify.com/CVE-2026-32625/): LibreChat Exfiltrates Server Secrets via MCP Server URL Injection (critical 9.6)
- [CVE-2024-11167](https://insights.sbomify.com/CVE-2024-11167/): Improper Access Control in danny-avila/librechat (critical 9.4)
- [CVE-2026-22252](https://insights.sbomify.com/CVE-2026-22252/): LibreChat MCP Stdio Remote Command Execution (critical 9.1)
- [CVE-2025-69222](https://insights.sbomify.com/CVE-2025-69222/): LibreChat is vulnerable to Server-Side Request Forgery due to missing restrictions (critical 9.1)
- [CVE-2024-41704](https://insights.sbomify.com/CVE-2024-41704/): Path traversal in n/a (critical 9.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-31951 and fix it if it is affected.

What it is: CVE-2026-31951 is a medium-severity vulnerability in Librechat Librechat, published on 27 Mar 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-31951 exists.

Affected product: Librechat Librechat. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-31951/ (Markdown: https://insights.sbomify.com/CVE-2026-31951/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-31951
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31951
- OSV: https://osv.dev/vulnerability/CVE-2026-31951

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-31951/
Summaries are generated and may contain mistakes; the official description above is the record.